1. Field of the Invention
This invention relates generally to the determination of various parameters in a subsurface formation penetrated by a wellbore, and, more particularly, to such determination by means of a remotely deployed sensor.
2. Description of the Related Art
Present day oil well operation and production involves continuous monitoring of various subsurface formation parameters. One aspect of standard formation evaluation is concerned with the parameters of reservoir pressure and the permeability of the reservoir rock formation. Continuous monitoring of parameters such as reservoir pressure and permeability indicate the formation pressure change over a period of time, and is essential to predict the production capacity and lifetime of a subsurface formation. Present day operations obtain these parameters either through wireline logging via a "formation tester" tool or through drill stem tests. Both types of measurements are available in "open-hole" or "cased-hole" applications, and require a supplemental "trip", in other words, removing the drill string from the wellbore, running a formation tester into the wellbore to acquire the formation data and, after retrieving the formation tester, running the drill string back into the wellbore for further drilling. Thus, it is typical for formation parameters, including pressure, to be monitored with wireline formation testing tools, such as those tools described in U.S. Pat. Nos.: 3,934,468; 4,860,581; 4,893,505; 4,936,139; and 5,622,223.
The '468 patent, assigned to Schlumberger Technology Corporation, the assignee of the present invention, describes an elongated tubular body that is disposed in an uncased wellbore to test a formation zone of interest. The tubular body has a sealing pad which is urged into sealing engagement with the wellbore at the formation zone by secondary well-engaging pads opposite the scaling pad and a series of hydraulic actuators. The body is equipped with a fluid admitting means, including a movable probe, that communicates with and obtains samples of formation fluids through a central opening in the sealing pad. Such fluid communication and sampling permits the collection of formation parameter data, including but not limited to formation pressure. The movable probe of the '468 patent is particularly adapted for testing formation zones exhibiting different and unknown competencies or stabilities.
The '581 and '139 patents, also assigned to the assignee of the present invention, disclose modular formation testing tools that provide numerous capabilities, including formation pressure measurement and sampling, in uncased wellbores. These patents describe tools that are capable of taking measurements and samples at multiple formation zones in a single trip of the tool.
The '505 patent, assigned to Western Atlas International, Inc., similarly discloses a formation testing tool capable of measuring the pressure and temperature of the formation penetrated by an uncased wellbore, as well as collecting fluid samples, at a plurality of formation zones.
The '223 patent, assigned to Halliburton Company, discloses another wireline formation testing tool for withdrawing a formation fluid from a zone of interest in an uncased wellbore. The tool utilizes an inflatable packer, and is said to be operable for determining in situ the type and the bubble point pressure of the fluid being withdrawn, and for selectively collecting fluid samples that are substantially free of mud filtrates.
The tools and methods described in the '468, '581, '139, '505, and '223 patents mentioned above are not intended for use in cased wellbores, and are generally not permanently connected to the wellbore or formation. However, formation testing tools and methods that are intended for use in cased wellbores are well known in the art, as exemplified by U.S. Pat. Nos.: 5,065,619; 5,195,588; and 5,692,565.
The '619 patent, assigned to Halliburton Logging Services, Inc., discloses a means for testing the pressure of a formation behind casing in a wellbore that penetrates the formation. A "backup shoe" is hydraulically extended from one side of a wireline formation tester for contacting the casing wall, and a testing probe is hydraulically extended from the other side of the tester. The probe includes a surrounding seal ring which forms a seal against the casing wall opposite the backup shoe. A small shaped charge is positioned in the center of the seal ring for perforating the casing and surrounding cement layer, if present. Formation fluid flows through the perforation and seal ring into a flow line for delivery to a pressure sensor and a pair of fluid manipulating and sampling tanks.
The '588 patent, also assigned to the assignee of the present invention, improves upon the formation testers that perforate the casing to obtain access to the formation behind the casing by providing a means for plugging the casing perforation. More specifically, the '588 patent discloses a tool that is capable of plugging a perforation while the tool is still set at the position at which the perforation was made. Timely closing of the perforation(s) by plugging prevents the possibility of substantial loss of wellbore fluid into the formation and/or degradation of the formation. It also prevents the uncontrolled entry of formation fluids into the wellbore, which can be deleterious such as in the case of gas intrusion.
The '565 patent, also assigned to Schlumberger Technology Corporation, describes a further improved apparatus and method for sampling a formation behind a cased wellbore, in that the invention uses a flexible drilling shaft to create a more uniform casing perforation than with a shaped charge. The uniform perforation provides greater reliability that the casing will be properly plugged, because shaped charges result in non-uniform perforations that can be difficult to plug, often requiring both a solid plug and a non-solid sealant material. Thus, the uniform perforation provided by the flexible drilling shaft increases the reliability of using plugs to seal the casing. Once the casing perforations are plugged, however, there is no means of communicating with the formation without repeating the perforation process. Even then, such formation communication is possible only as long as the formation tester is set in the wellbore and the casing perforation remains open.
Each of the aforementioned patents is therefore limited in that the formation testing tools described therein, whether for use in open or cased holes, are only capable of acquiring formation data as long as the wireline tools are disposed in the wellbore and in physical contact with the formation zone of interest. Since "tripping the well" to use such formation testers consumes significant amounts of expensive rig time, it is typically done under circumstances where the formation data is absolutely needed or it is done when tripping of the drill string is done for a drill bit change or for other reasons.
During well drilling activities, the availability of reservoir formation data on a "real time" basis is a valuable asset. Real time formation pressure obtained while drilling will allow a drilling engineer or driller to make decisions concerning changes in drilling mud weight and composition as well as penetration parameters at a much earlier time to thus promote the safety aspects of drilling. The availability of real time reservoir formation data is also desirable to enable precision control of drill bit weight in relation to formation pressure changes and changes in permeability so that the drilling operation can be carried out at its maximum efficiency.
It is desirable therefore to provide a method and apparatus for well drilling that enable the acquisition of various formation data from a subsurface zone of interest while the drill string with its drill collars, drill bit and other drilling components are present within the well bore, thus eliminating or minimizing the need for tripping the well drilling equipment for the sole purpose of running formation testers into the wellbore for identification of these formation parameters.
It is a further object of the present invention to provide a rugged structure for intelligent data sensors that are adapted for deployment into the formation, whereby the sensors may be reliably exposed to high g-forces during the deployment process with an expectation of survival and continuous functional integrity.
It is a further object of the present invention to provide a structure for such sensors, whereby the sensors may be reliably exposed to the high pressures and temperatures of an ignition-induced propulsive force during deployment.
It is a further object to provide and apparatus and method of operating such sensors, whereby the sensors are adapted to survive the launch from a gun-like deployment mechanism without deformation, damage, or failure.
It is still a further object to provide an apparatus and method of operating such sensors, whereby the sensors survive impact in a subsurface rock formation without deformation, damage, or failure.
It is still a further object to provide an apparatus and method of operating such sensors, whereby the sensors achieve substantially linear penetration to a satisfactory depth in the formation.
It is still a further object to provide an apparatus and method of operating such sensors, whereby the sensors are capable of radio frequency communication through the rock formation.